Turning relay on and off every 5 seconds

Projects Programming
1

Trying to have my relay turn on and off every 5 seconds.

#define relayPin 6
unsigned long previousMillis = 0UL;
unsigned long interval = 10000UL;

String readString;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(relayPin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  unsigned long currentMillis = millis();
  
  Serial.println(currentMillis - previousMillis);

  while (Serial.available() ) {
    delay(10);
    if (Serial.available() > 0) {
      char c = Serial.read();
      if (c == ',') {
        break;
      }
      readString += c;
    }
     if (readString.length() > 0) {
    Serial.println(readString); //prints string to serial port out

    if (readString.indexOf("w") >= 0) {
      if (currentMillis - previousMillis < interval / 2) {
        Serial.println("RELAY ON");
      digitalWrite(relayPin,HIGH);
      previousMillis = currentMillis;
      }
      

    }
    if (readString.indexOf("s") >= 0) {                      
      Serial.println("RELAY OFF");
      digitalWrite(relayPin,LOW);
    }
  }
  readString = "";
  }
}
2

Hello,

What’s your question ?
Why are you reading the serial port?

do yourself a favour and help us help you fl! please read How to get the best out of this forum and post accordingly

3

Reading the serial port to send commands from the serial monitor because I don't use buttons.

4

The shown code has nothing to do with your assignment.

5

If you have 1 char commands there is no need to build a string, just check if the char you get matches one of the commands

6

what are the commands? How are they related to the task at hand?

7

The test for whether the current timing period has ended depends on Serial data being available. How long will such data be available and what happens if nothing is available ?

8

Originally it was starting the relay on and off with "w" and "s" commands.

9

:slight_smile:
Why are you asking something completely different?

10

Something like this

bool relayIsBlinking = false;

… // other variables and setup()

void loop() {
  switch(Serial.read()) {
    case 's': relayIsBlinking = true; break; // possibly initialize timing variables etc 
    case 'w': relayIsBlinking = false; break;// possibly turn it off depending if you want to keep the last state or not
    default: break; // ignore anything else
  }

  if (relayIsBlinking) {
    // handle the blinking 
    …
  }
}

To handle the blinking study blink without delay, one of the available example in the IDE.

For extra information and examples using millis look at

3 Likes
11

This code does

turn on/off the relay every 5 seconds
5 seconds on
5 seconds off
repeat

The explanation of this code is similar to your description:
almost non-existant.

unsigned long MyRelayTimer = 0; // Timer-variables MUST be of type unsigned long
const byte    relayPin = 6;
const byte    OnBoard_LED = 13;


void setup() {
  Serial.begin(115200);
  Serial.println("Setup-Start");
  PrintFileNameDateTime();
}


void loop() {
  BlinkHeartBeatLED(OnBoard_LED,250);

  if ( TimePeriodIsOver(MyRelayTimer,5000) ) {
    digitalWrite(relayPin, !digitalRead(relayPin) );
  }  
}


void PrintFileNameDateTime() {
  Serial.println( F("Code running comes from file ") );
  Serial.println( F(__FILE__) );
  Serial.print( F("  compiled ") );
  Serial.print( F(__DATE__) );
  Serial.print( F(" ") );
  Serial.println( F(__TIME__) );  
}


// easy to use helper-function for non-blocking timing
boolean TimePeriodIsOver (unsigned long &startOfPeriod, unsigned long TimePeriod) {
  unsigned long currentMillis  = millis();
  if ( currentMillis - startOfPeriod >= TimePeriod ) {
    // more time than TimePeriod has elapsed since last time if-condition was true
    startOfPeriod = currentMillis; // a new period starts right here so set new starttime
    return true;
  }
  else return false;            // actual TimePeriod is NOT yet over
}


void BlinkHeartBeatLED(int IO_Pin, int BlinkPeriod) {
  static unsigned long MyBlinkTimer;
  pinMode(IO_Pin, OUTPUT);
  
  if ( TimePeriodIsOver(MyBlinkTimer,BlinkPeriod) ) {
    digitalWrite(IO_Pin,!digitalRead(IO_Pin) ); 
  }
}

if this is not what you want to have. There is no way around describing with more precision and more details what you really want to have

best regards Stefan

1 Like
12

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